A. Field of the Invention
The present invention relates to surface coatings, and more particularly to methods and compositions for producing inorganic coatings on decorative, organic surfaces that are vulnerable to environmental exposure.
B. Description of the Related Art
Surfaces exposed to environmental degradation--that is, to the effects of light, heat, ambient chemicals and mechanical abrasion--are frequently protected by various types of surface treatments. These include application of galvanic coatings, electrochemical oxidation (anodization), and simply coating with paint. The surface-treated article typically exhibits not only greater resistance against environmental damage, but also improved aesthetic appearance.
Although the methods of applying conventional surface treatments have improved in recent years, the basic technologies have not; for example, the ingredients used in nickel plating, anodizing and painting are still essentially the same.
Unfortunately, the protection afforded by conventional surface treatments is of limited duration. Colors fade when exposed to light (particularly the highly energetic ultraviolet radiation present in sunlight); and coatings erode when exposed to airborne acids, they scratch when abraded by hard objects, and peel when subjected to cyclical weather-related thermal patterns (due to repeated expansion and contraction). Even when newly applied, the strength and stress durability of traditional coatings tends to be less than optimal.
These shortcomings are due to the nature of the materials used and the sometimes contradictory requirements of different surface coatings. Decorative effects are generally produced by layers that exhibit a particular color or otherwise hide the surface appearance of the underlying substrate; whether pigmented or dye-based, such layers usually contain organic constituents that are relatively labile. While these layers are sometimes coated with a tougher, transparent material (such as a sealer), the conditions necessary to deposit truly refractory inorganic coatings are usually incompatible with the physical and chemical susceptibilities of the decorative layer, such as deposition temperature and/or reaction with deposition gases.
Typically, the decorative layer emits exudates such as gases, vapors and low-molecular-weight plasticizers during drying; the rate of emission tends to increase significantly as the ambient temperature is raised. However, refractory inorganic coatings typically have high melting points and, consequently, such coatings must generally be applied at elevated temperatures. Because such temperatures substantially exceed the melting points of typical paints and plastic surface materials, application of such a coating to an ordinary colored layer would both degrade the colored layer and cause unwanted diffusion between the layers. In the case of application to a painted surface, the high emission rate of the latter would also interfere with proper composition and curing of the inorganic layer.